RICHLAND — Electric cars account for fewer than 0.05 percent of passenger vehicles in the United States today, but Michael Kintner-Meyer envisions a future where plug-ins rule the roads.

The proliferation of electric cars will bring benefits — like lower tailpipe emissions — ­but could also create unique headaches, says Kintner-Mayer, who leads a project at Pacific Northwest National Laboratory to improve the vehicles and tackle the problems.

Now, he and his colleagues have crafted a solution to the scenario that gives power-grid operators nightmares: The prospect that millions of Americans will get home from work and plug in their cars at the same time.

“It would create havoc,” said Kintner-Meyer. “You could have the lights go out. You could have rolling brownouts.”

The way to avoid widespread overloads is to spread out the demand — which is what PNNL’s “grid-friendly” charger does. The device, which is about the size of a shoebox, monitors the status of the grid and adjusts accordingly, switching off when demand is high and switching on when power is plentiful.

Adaptive charging could lower car owners’ electricity bills by allowing them to draw power when rates are lowest. And if enough cars use the systems, they could also collectively provide a valuable service to the power grid by dampening swings in electrical generation from the growing number of wind farms and solar arrays.

Drivers could save up to $150 a year, the grid would be protected from crashing, and the overall power system would run more smoothly, Kintner-Meyer said.

California-based AeroVironment, Inc. licensed the technology from PNNL and is integrating it into beta versions of a charging station. Alec Brooks, the company’s chief technology officer for efficient energy systems, has been using one to charge his Nissan Leaf.

At PNNL, Kintner-Mayer runs the system on a 2009 Prius hybrid that he and his team converted to a plug-in.

Because the grid-friendly system switches off and on, it takes longer than a conventional charging system, Brooks said. But it doesn’t matter — as long as the car is fully charged in the morning.

“There’s usually plenty of slack time,” he said. “I can’t think of the last time I was waiting for my vehicle to charge.”

Owners in a hurry can simply bypass the grid-friendly feature.

With fewer than 150,000 electric cars in the nation, power-grid operators don’t have much to worry about yet. But plug-in cars are the fastest-growing sector of the automotive industry, according to the advocacy group Plug In America.

The Northwest is helping lead the charge, with 5,400 electric cars in Washington and about 3,000 in Oregon. The nation’s highest-selling Leaf dealership is in Bellevue, said Redmond resident Chad Schwitters, an electric-car enthusiast and vice president of Plug in America.

AeroVironment operates what’s called the West Coast Electric Highway — a network of fast-charging stations that will soon number 55, situated along I-5 and other highways in Washington and Oregon.

The Northwest is also ahead of the rest of the nation in experiencing growing pains caused by the proliferation of wind farms. In 2011, the Bonneville Power Administration ordered some turbines to shut down because the region had more power than it knew what to do with.

Now, grid operators usually compensate for swings in power by adjusting the spill at hydropower dams or having power plants increase or decrease their power output, Brooks explained. “Power plants get paid to do that.”

But if large numbers of electric cars were hooked into grid-friendly chargers, they could soak up excess electricity, then power down when the grid is running low, he explained.

There’s no billing arrangement yet that would allow electric-car owners to be compensated for helping even out the grid. But Brooks predicts that could change, which would provide a powerful incentive to switch to grid-friendly charging stations.

“I think it can be a very large market once there’s a recognition that you’re providing a useful service to the grid,” he said.